php根据某年某月获取该月天数的三种方法

$d=cal_days_in_month(CAL_GREGORIAN,10,2017);
echo("There was $d <br /><br />");

$i=10;
$y=2017;
echo date("t",strtotime("$y-$i"));

function get_day( $date )   
{
    $tem = explode('/' , $date);       //切割日期  得到年份和月份
    $year = $tem['0'];
    $month = $tem['1'];
    if( in_array($month , array( 1 , 3 , 5 , 7 , 8 , 01 , 03 , 05 , 07 , 08 , 10 , 12)))
    {
        $text = $year.'年的'.$month.'月有31天';
    }
    elseif( $month == 2 )
    {
        if ( $year%400 == 0  || ($year%4 == 0 && $year%100 !== 0) )        //判断是否是闰年
        {
            $text = $year.'年的'.$month.'月有29天';
        }
        else{
            $text = $year.'年的'.$month.'月有28天';
        }
    }
    else{
 
        $text = $year.'年的'.$month.'月有30天';
    }
    return $text;
}
$i=10;
$y=2017;
echo get_day($y.'/'.$i);